Why does phase 1 only include GS-14 or equiv. and not GS-15s? I assume, but need to validate, -> GS-15s are already at the top of what we can control, to move up they will go to SES boards, etc.?

The purpose of the phased approach to mandate is to ensure that the raters and SRs are not overwhelmed with a new process/procedure applicable to so many all at once. The GS14 population was targeted simply because they are the traditional (not exclusive) applicants for the BQ boards. All others are not prohibited from completing this cycle, regardless of board application intent, they are simply not required unless applying for a BQ board.